The invention concerns a device for removal of condensate from a steam-heated, rotatable drying cylinder, and more specifically, a steam-heated, rotatable drying cylinder of the type used on paper machines for drying a freshly produced web.
Among those familiar with the art such a device for condensate removal is generally termed a "rotating syphon." This design has the advantage that no relative movement takes place between the rotating drying cylinder and the siphon because the siphon is rigidly mounted in the drying cylinder so that both rotate jointly. In another prior design, the siphon is fixed so that it does not participate in the rotary movement of the drying cylinder.
Rotating siphons employ various designs for the suction mouthpiece. For instance, it may have a shape approximating a plate such as in U.S. Pat. No. 3,034,225, or it may have a shape approximating a bell such as in U.S. Pat. No. 2,993,282. Additionally, the suction mouthpiece, which may also be designed as a box, may be provided with a funnel-type suction snout opening in the direction of rotation such as in U.S. Pat. No. 2,892,264. Such a snout facilitates the condensate removal from the drying cylinder especially when the drying cylinder is rotating at a relatively low speed permitting the condensate to form a sump, while otherwise when the drying cylinder is rotating at higher operating speeds the condensate lies as a ring-shaped film on the inside surface of the cylinder shell.
Previously known from the German Patent Publication No. 14 61 125 (which is the counterpart to U.S. Pat. No. 3,264,754) is a suction mouthpiece having the shape of a flat nozzle. The slot-shaped inlet opening extends parallel with the direction of rotation. The condensate influx can be promoted by inclined surfaces having an inclination which is axially parallel with the inside surface of the shell.
The condensate removal is in all cases effected by adjusting inside the drying cylinder a pressure higher than in the condensate suction pipe including the suction mouthpiece. Thus, part of the supplied steam flows constantly through the rotating siphon mixing with a certain amount of the condensate and moving it outside.
To enhance the conveying effect on the condensate, a side channel for feeding additional steam may be provided at the transition from the suction mouthpiece into the condensate suction pipe. Previously known from U.S. Pat. No. 2,993,282 or German Patent Publication 14 61 125, this side channel is presented by simply providing a bore extending through the wall of the suction mouthpiece.
In U.S. Pat. No. 2,993,282 it is known to arrange in the bell-shaped suction mouthpiece an insert which has the shape of a partitioning wall which extends parallel with the axis of rotation of the cylinder. This partitioning wall guides the condensate into the interior of the suction mouthpiece. According to U.S. Pat. No. 4,384,412, the partitioning wall may be given the shape of a wedge, as viewed in cross section, to improve the deflection effect.
Many of these prior designs have proved themselves in practice when the drying cylinder is being operated at various operating speeds wherein the condensate sometimes forms a ring and sometimes a sump. But under certain unusual conditions, especially when the normal operation is somehow interrupted, these earlier devices have failed to remove the condensate. Under these conditions the drying cylinder is said to be "flooded" i.e., it fills up increasingly with condensate. In extreme cases, the drying cylinder is filled with condensate almost up to the axis of rotation.